It doesn't work that way.
"Nr 1" vs "Nr 1" followed by "Nr 2 vs Nr 2", etc etc lasts one time through the rotation. Maybe twice through, if everything lines up perfectly. Perhaps again right after the AS break.
After that, due to rain outs, differing schedules, injuries, etc etc it's random chance for the other 90 percent of the season. You're as likely to get the other guys "Nr 1" vs your "Nr 5" as "5 vs 5."
Get the best starters you can. Get 5 "Nr 1's." Heck, get 8 of them, since you'll need at least 8 starters to get through most seasons, sometimes more.
"He's just a number 5 starter" reminds me of "he's just fine because he'll bat 9th."
Faulty logic.